The present invention relates to improvements in methods and apparatus for making bags, and more particularly to using a forming, filling and sealing method where a continuous sheet of plastic is fed downwardly over a filling tube and filled and cross-sealed.
A common method of making bags, such as of thermoplastic containing product materials is by use of vertical forming, filling and sealing apparatus. Such apparatus takes a continuous flat sheet of plastic material which is fed forwardly and passed downwardly over a shaping shoulder and then shaped into tubular form by being wrapped around a vertical forming axis. The edges of the sheet are joined, such as by heat sealing them to each other or by being attached by joining continuous zipper strips which are secured to the edges of the sheet.
A product to be contained in the bag, such as a foodstuff, is introduced by dropping through the filling tube to be discharged at the opening into the tubular formed thermoplastic. The sheet is pulled downwardly over the filling tube in bag lengths, and as the contents are dropped into the bag through the filling tube, a cross-seal is formed above the contents and the preformed bag is cut from the bottom. The cross-seal then closes the plastic bag tube so that contents can be dropped for another bag. Earlier forms of such mechanism are shown in U.S. Pat. Nos. 3,815,317 and 4,355,494.
It is important in the formation of the bag that the cross-seams be leak-proof so as to protect the bag contents. It is also desirable, particularly where a transparent or highly visible plastic is employed, to form a cross-seal which is not replete with wrinkles and which preferably is wrinkle-free. This is desirable from an appearance standpoint, but also from the standpoint of insuring that the cross-seaming apparatus does not engage bunched up or wrinkled material and adversely affect the uniformity of the seam across the tubular sheet material.
As the cross-seal is formed and a completed bag is cut off of the length of tubing, contents are dropped through the filling tube down into the cross-sealed end. The exposed film can be slit of punctured as the sharp product rubs the film during the fall when the product impacts against the film. Any puncturing or damage to the film would not be tolerable because it would create a defective leaking package.
It is accordingly an object of the present invention to provide an improved method and apparatus for forming bags in a form, fill and seal operation wherein cross-seams can be effectively and efficiently made to achieve a seam on a bag which is essentially free of wrinkles and has a good appearance.
A further object of the invention is to provide a method and apparatus for cross-seaming bags in a form, fill and seal machine wherein the completed bag is more attractive and better made than with methods and apparatus heretofore available.
A still further object of the invention is to provide an improved method of making cross-seams on bags in a form, fill and seal machine wherein the apparatus is relatively simple in construction and reliable in operation.
It is a further object of the invention to provide an improved method and apparatus for making and filling bags in a vertical form, fill and seal machine wherein the possibility of damage to the package from the product being dropped against the film during filling is eliminated.